Pilot operated unloading valve



Det. 9, 1959 R, F, HoDGsoN ETAL 3,482,590

PILOT OPERATED UNLOADING. VALVE Filed March 18, 196e 2 sheets-sheet 1 Robert F. Hodgson a Arhur J. Williams Dec 9, 1969 R. F. HoDGsoN ET AL 3,482,590

BILOT OPERATED UNLOADING'.L VALVE Fig.2.

Robert F. Hodgson Arthur J. Williams United States Patent O U.S. Cl. 137-108 8 Claims ABSTRACT F THE DTSCLSURE A pilot operated unloading valve having a pair of inlets for receiving pressurized fluid from different sources. At low pump pressure when the valve is in neutral position, downstream flow of fiuid from a first source will be permitted while the ow from the second source will be diverted back to reservoir. When pressure increases in the hydraulic system, as when the flow from the first source is directed to a work cylinder, a pilot valve will shift to cause flow from the second source to combine with that of the first source. At a predetermined high pressure the pilot valve will shift to another position to divert the fiow from the second source back to reservoir while permitting the flow from the first source to continue downstream. Combined flow will be restored at a pressure below the predetermined high pressure.

This invention relates to a hydraulic unloading valve and particularly to an automatic pilot operated unloading valve adapted to be connected with multiple sources of pressurized fiuid and which under certain conditions will permit downstream fiow of one of the sources While diverting the flow of other sources and under different conditions to permit combined downstream fiow of all of the sources.

In operating certain apparatus, it is desirable to have a hydraulic control system capable of providing in some instances, and high pressure-low fluid flow for doing work, in other instances. When operating a front end loader, for example, it is desirable to be able to lift an empty bucket quickly. This quick lifting would require a high quantity of fluid fiow to the actuating cylinder for the bucket. When the bucket is directed to do work, as in scooping up a pile of soil, high pressure-low fiuid fiow would be adequate for the actuating cylinder. In order to get high quantity of fiuid flow two or more pumps are oftentimes used in the hydraulic system. At least one of these pumps can provide the necessary pressure for doing the bucket work. The flow from the other pump or pumps will be diverted to the system reservoir during high pressure low flow conditions. This diverting to reservoir of fiow from a pump is commonly known as unloading of the pump. Heretofore, complicated circuits were provided to perform pump unloading, adding to an already complex hydraulic circuit. To eliminate adding circuit upon circuit, attempts have been made to construct unloading valves for incorporation into a single circuit. Two prominent problems are inherent in the known unloading valves. The first of these problems is the inability of these valves to unload at low pressures. Low pressure unloading is desirable when the control valves are all in neutral, as when a front end loader is sitting at idle. The neutral control valves due to their construction will place a pressure-demand on the pumps. One pump could fulfill this low pressure flow demand. By subjecting all of the pumps to Athis low pressure demand, (i) the pump drive is placed under an unnecessary horsepower requirement, and (ii). the pumps will tend to overheat. The second of the prominent unloading valve problems is valve hunting `at high pressure unloading. The functioning of a typical unloading 3,482,590 Patented Dec. 9, 1969 valve during high pressure unloading operation in a two pump hydraulic system of a front loader will best illustrate hunting. When high pressure low flow is required, as determined by a preselected high pressure low flow, a valve element will shift to open a diversion path to the unloaded pump while permitting the downstream fiow of the work pump. Say for example, the unloading pressure is 1500 p.s.i., the bucket meets the resistances of a pile of Soil and pressure above 1500 p.s.i. is needed on the actuating cylinder to overcome this resistance. One pump will be diverted and the other Will pump fiuid into the actuating cylinder, lf the resistance of the soil diminishes for some reason and demands slightly below 1500 p.s.i. to overcome, the valve will shift and combined downstream fiow of both pumps will result. If the bucket encounters the higher resistances again, the valve will shift to divert pump fiow. When this shifting of the valve becomes regular, as would happen if the soil resistance demanded just about 1500 p.s.i. to overcome, the valve is said to be hunting That is, it doesnt know which way to shift. This hunting is characterized by chattering noises and a shaking of the vehicle. Not only are effects of the hunting annoying to operating personnel, but damage to the unloading valve, and control Valves, and other components in the hydraulic system and on the vehicle could result therefrom.

We provide a new hydraulic unloading valve which overcomes the deficiencies of the old unloading valves. Our unloading valve permits both high and low pressure unloading with a single pilot valve within a single valve assembly. Furthermore, our unloading valve reseats from high pressure unloading at a pressure safely below the high unloading pressure to thereby eliminate valve hunting. We provide these results and others with an unloading valve which, preferably, comprises, a valve body having a first inlet means adapted to be connected with a first source of pressurized fluid and second inlet means adapted to be connected with a second source of pressurized fluid; a passageway communicating between the first and second inlet means; pressure responsive closure means in the passageway for yblocking communicating between the first and second inlet means; outlet means communicating with the first inlet means; a first cylinder intersecting the second inlet means; a second cylinder spaced from the first cylinder; an exhaust passage communicating between the first and second cylinders; a downstream open first branch passage communicating with said first inlet means and having a parallel flow path communicating with one end portion of the second cylinder; a second branch passage communicating between one end portion of the first cylinder and an intermediate portion of the second cylinder; pressure responsive piston means shiftable in the first cylinder and having a first bore communicating between the second inlet means and the other end portion of the first cylinder and a second bore communicating between the second inlet means and the one end portion of the first cylinder; pilot valve means shiftable in the second cylinder and responsive to first, second, and third progressively increasing fluid pressures in the first inlet means to be oriented when the pressure in the inlet means is below the first fluid pressure in a first position to connect the second branch passage through the second cylinder and thereby cause the piston to be positioned for connecting the second inlet means with the exhaust passage while causing the closure means to close to block communication `between the first and second inlet means, and further responsive to be oriented when the pressure in the first inlet means reaches the first fluid pressure in a second position to block communication between the second branch passage and the exhaust passage and thereby cause the piston in the first cylinder to be positioned to block communication between the second inlet means and the exhaust passage while causing the closure means to open to connect the second and first inlet means, and yet responsive to be oriented in a third position when the third fiuid pressure is reached to connect the second branch passage with the exhaust passage to thereby cause the piston to be positioned for connecting the second inlet means with the exhaust passage while causing the closure means to close to block communication between the rst and second inlet means, and still yet responsive to be oriented in the second position when the pressure in the first inlet means decreases from the third fiuid pressure to the second fluid pressure.

Other details, objects and advantages of the invention will become apparent as the following description of a present preferred embodiment thereof proceeds.

In the accompanying drawings we have shown a present preferred embodiment of the invention in which:

FIGURE 1 is a sectional view of the unloading valve of the present invention showing the orientation of elements thereof under one fiuid flow condition;

FIGURE 2 is a View along the lines II-II of FIG- URE 4;

FIGURE 3 is a sectional view of the valve in FIGURE 1 showing the orientation of elements thereof under another uid fiow condition; and

FIGURE 4 is a sectional view of the valve of FIG- URE 1 showing the orientation of elements thereof under yet another fiuid fiow condition.

Referring now to the drawings wherein like reference numerals refer to like parts throughout the various views, refers generally to a piiot operated unloading valve including an elongated valve body 12 adapted to be connected with a bank of series, parallel, or priority hydraulic valve sections such as the valve sections described in co-pending U.S` patent, granted July 4, 1967. Valve body 12 is provided with a first inlet chamber 14 extending transversely inwardly from a lateral side of the body, which inlet chamber 14 is adapted to be connected with a source of pressurized fiuid. A longitudinal bore 16 extends from the left end, as viewed in the figures, of body 12 and intersects inlet chamber 14. A transversely extending outlet chamber 18 intersects bore 16 and communicates with inlet chamber 14. A transversely extending exhaust chamber 19 intersects bore 16 leftwardly of outlet chamber 18 and communicates with inlet chamber 14 through longitudinally extending passageway 20. A pressure responsive relief valve 21 of any well known type extends from a left end portion of Ibody 12 through a portion of exhaust chamber 19, in passageway 20, and into a portion of inlet chamber 14. Under normal circumstances fluid flow between inlet chamber 14 and exhaust chamber 19 will be blocked. A downstream open parallel flow outlet chamber 22 communicates with inlet chamber 14 and extends outwardly from a closed end lying in a vertical plane passing intermediate the face of body 12 to an open end in one of the faces of body 12.

A second inlet chamber 24 extends inwardly from one face of body 12 and is adapted to be connected with a source of pressurized fiuid. Preferably, inlet chamber 24 will be connected with a source different from that connected with the first inlet chamber 14. A passage 25, forming part of bore 16, connects the second inlet chamber 24 with the first inlet chamber 14. A check valve 27 extends from a left end portion of body 12 through bore 16 and into passage 25 where the end of check valve 27 abuis a cylindrical sleeve 33 snugly received in passage 25. Check valve 27 is pressure responsive, that is, it will open when the fiuid pressure in second inlet chamber 24 reaches a predetermined value. Check valve 27 can be any kind of well known pressure responsive check valve. We have here illustrated a check valve 27 received in an elongated cylindrically shaped body 28 having a hollow inner portion 29 adapted to receive a helical coil spring 30 urging a force on the valve 27 which force is sufiicient f 4 to position the valve 27 rightwardly of the free end of body 28 and into abutment with sleeve 33. Thus, check valve 27 blocks fluid flow between second inlet chamber 24 and first inlet chamber 14.

A first cylinder 35 extends transversely through the body 12 and is closed at either end by plugs 36 and 37 suitably, sealably received therein. Cylinder 35 intersects second inlet chamber 24. A piston 39 is suitably slidably received in cylinder 35 and, as viewed in the figures, has a hollow lower end portion 40 for suitably receiving a helical coil spring 41 to urge an upwardly directed force between plug 36 and piston 39. Piston 39 is also provided with a first bore 42 communicating between the second inlet chamber 24 and the hollow portion 40 and a second bore 43 communicating between second inlet chamber 24 and the upper end portion 44 of cylinder 3S. Piston 39 is further provided with a reduced diameter outer intermediate section 45.

A second cylinder 47 extends transversely through body 12 and is spaced rightwardly of the first cylinder 35. A plug 48 suitably sealably received in second cylinder 47 forms the bottom end thereof. An exhaust chamber 49 extends transversely between the faces of body 12 and is disposed between the first and second cylinders 35 and 47. Exhaust chamber 49 intersects both cylinders 35 and 47. A branch passage 51 extends from first inlet chamber 14 to first cylinder 35 around the body of piston 39 and to a branch chamber 52 and then through an orifice 53 into a lower portion of second cylinder 47. Another branch passage 55 extends between a lower end portion of first cylinder 35 to an intermediate chamber portion 56 of second cylinder 47.

A pilot valve assembly 58 is suitably slidably received in second cylinder 47 and includes a hollow retainer cap 59 suitably sealably received in the upper end portion of second cylinder 47 and extends downwardly to a horizontal plane which passes through exhaust chamber 49. A series of circumferentially spaced openings 60 extends through a lower end portion of retainer cap S9 to cornmunicate between second cylinders 47 and the interior of retainer cap 59. A hollow spool 61 is disposed in the lower end portion of second cylinder 47 and is provided with chamber 62 therethrough which chamber has a lower section 62a and intermediate section 62b smaller diameter than 62a and an upper section 62C of larger diameter than 62b. A plug 63 is suitably received in upper section 62C and intermediate the extremes thereof to define an upper space 62C' and a lower chamber 62C". The plug 63 has a central bore 64 having a diameter substantially the same as that of intermediate section 62b of chamber 62. A plurality of circumferentially spaced openings 65 extend through an intermediate 'portion of spool 61 to communicate between chamber 56 of second cylinder 47 and chamber 62C within spool 61. An opening 66 eX- tends through a lower end portion of spool 61 to cornmunicate between a lower portion of second cylinder 47 and lower section 62a within spool 61. A pilot valve element 68 is suitably slidably received in chamber 62 within spool 61 and has separated upper end portion 69 extending upwardly of spool 61 to a point in a lower end portion of retainer cap 59. Upper end portion 69 of pilot valve element 68 has an outer diameter slightly less than the inner diameter of bore 64 of plug 63. Upper end portion 69 extends downwardly to an intermediate portion 70 which begins at 'a point just below the upper surface of plug 63. Intermediate portion 70 is provided with a pair of diametrically opposed flats 70a. A pair of opposed passageways is thus formed around intermediate portion 70 extending from chamber 62C" and terminating at upper end portion 69, when pilot valve element 68 is disposed as illustrated in FIGURE 1. Intermediate portion 70 extends downwardly to abut with a lower portion 71 vhaving a diameter slightly greater than portion 70, which lower portion '71 begins at point just above interv mediate section 62h of chamber 62. The outer diameter of lower portion 71 is also slightly less than the inner diameter of intermediate section 62h. Lower portion 71 extends downwardly to an end portion 72 which begins in lower section 62a at a point just below intermediate section 62b. End portion 72 has an outer diameter slightly less than the inner diameter of lower section 62a and extends downwardly to a horizontal plane including the lower end of spool 61.

The outer upper end portion of spool 61 is provided with a pair of diametrically opposed flats and thereby providing opposed open passageways 74 communicating between chamber 56 and exhaust chamber 49 when the spool 61 is in the position illustrated in FIGURE l. As shown in FIGURE 2 the spool 61 will block the communication between chamber 56 and exhaust chamber 49.

A plunger element 77 is suitably fixed to the greater part of the upper end portion 69 of pilot valve element 68. Plunger element 77 includes a central disc portion 78, the lower surface of which is disposed slightly above the upper end of spool 61, as illustrated in FIGURE l. An upper cylindrical portion 79 extends upwardly from the upper surface of disc portion 78, and a lower cylindrical portion 80 extends downwardly from central disc 78 into abutment with the upper surface of plug 63. A helical coil spring 82 extends between the upper surface of central disc portion 78 and the upper end of retainer cap 59. An adjustment screw 83 suitably supported by retainer cap 59 engages the upper end of spring 82.

The operation of the unloading valve just described is illustrated in FIGURES 1, 3 and 4. FIGURE 1 shows a condition where the downstream hydraulic valves are in neutral with the open center chambers being clear to receive upstream pump flow. Hydraulic fluid will be flowing through inlet chamber 14 out of outlet chamber 18 and parallel flow outlet chamber 22 and through the downstream valves. When the pumps in the hydraulic system are initially started the piston 39 is shifted upwardly under the urging of spring 41 to the same position shown in FIGURE 3. The check valve 27 will be urged leftwardly by the pressure in the second inlet chamber 24 and combined downstream flow from the first and second inlet chambers 14 and 24 will result. The pressure on the hydraulic system will build up rapidly to a rst pressure above which piston 39 will shift to the position shown in FIGURE l. Fluid will llow through the second bore 43 of piston 39 to pressurize the upper end portions 44 of first cylinder 35. Fluid will also flow from second inlet chamber 24 through the first bore 42 of piston 39 and will be at a lower pressure when it reaches chamber 40 than the pressure in the upper end portion of first cylinder 35. Spring 82 will urge a downward force on pilot valve assembly 58 to open a flow path between chamber 40 and exhaust chamber 49. Ac cordingly, the fluid flowing into chamber 40 will flow through branch passage 55 into chamber 56, through passageways 74 and into exhaust chamber 49. The pressure in chamber 40 will reduce to a low value and the fluid pressure in upper portion 44 of first cylinder 35 will act on piston 39 and overcome the preload of spring 41 and thereby cause piston 39 to shift into the position shown in FIGURE 1. The reduced intermediate portion 45 of piston 39 will be positioned to permit passage of fluid from the second inlet chamber 24 to exhaust charnber 49 and back to reservoir. The check valve 2.7 will move rightwardly to close flow passage between the second and yfirst inlet chambers. Therefore, only fluid from the first inlet chamber 14 will flow downstream.

In FIGURE 3 the condition prevails wherein downstream valves have their open centers blocked and work chambers open. Fluid will flow through inlet chamber 14 and out of outlet chambers 18 and 22 to work cylinders, or the like. The pressure in inlet chamber 14 will increase. Fluid will flow through branch passage 51 through orifice 53 and into lower end portion of second cylinder 47. The pressure buildup in second cylinder 47 will move spool 61 and pilot valve element 68 against the urging of spring 82. The spool 61 will move until it Teaches the lower end of retainer cap 59 at which point communication between lower end of first cylinder through branch passage to exhaust chamber 49 is blocked by spool 61. The pressure of the fluid entering the lower end of first cylinder 35 from second inlet chamber 24 will build up until it reaches the same pressure as the fluid in upper portion 44 and the spring force of spring 41 will urge piston 39 upwardly to a po-sition such that communication is blocked between second inlet chamber 24 and exhaust chamber 49. The fluid pressure in second inlet chamber 24 will overcome the spring force of spring 30 of check valve 27 to move it away from passage 25 and fluid will flow from second inlet chamber 24 through openings 32, into inlet chamber 14 to combine with the fluid therein and flow outwardly of body 12 through outlet chambers 18 and 22. It should be noted that the pressure buildup rate of the fluid in second inlet chamber 24 will be much lower than that in inlet chamber 14. This lower pressure buildup rate will dampen the possible hydraulic shocking of the system.

In FIGURE 4 a condition prevails where the downstream hydraulic valves are in the work position and the pump supplying fluid to second inlet chamber 24 is unloaded. The pressure in first inlet chamber 14 builds up to a third pressure. Fluid will be flowing from second inlet chamber 24 through first bore 42 in piston 39 into the lower portion of `first cylinder 35 out of branch passage 55 into chamber 56 through openings 65 and into chamber 62e within spool 61. The uid pressure in the lower portion of second cylinder 47 will increase as fluid Hows from first inlet chamber 14 to second cylinder 47. It should be noted at this time that the cross-sectional area of intermediate portion is designed to be smaller than that of lower portion 71 a magnitude such that when fluid pressure in the lower portion of second cylinder 47 reaches a predetermined value the pilot valve element 68 will shift upwardly overcoming the force of spring 82 and pressure in chamber 62C. When this upward movement of pilot valve element 68 occurs chamber 62C" will be opened to communicate between chamber 56 and exhaust chamber 49 as shown in FIGURE 4. Thus, the fluid in the lower portion of first cylinder 35 will flow to exhaust chamber 49, piston 39 will be urged downwardly under the pressure of the fluid entering upper end portion 44 of lfirst cylinder 35 through second bore 43 in piston 39. The second inlet chamber 24 will be connected with exhaust chamber 49 around the reduced intermediate section 45 of piston 39. Check valve 27 will be urged by spring 30 into passageway 25 to close second inlet chamber 24 to first inlet chamber 14. Thus, downstream fluid flow will be provided through first inlet chamber 14 while flow through second inlet chamber 24 will be diverted back to reservoir. It should be noted that the above described movement of the pilot valve element 68 due to the differential areas between lower portion 71 and intermediate portion 70 thereof results in a toggle type of motion to the unloading function. When chamber 62C" begins opening to permit fluid flow to exhaust chamber 49 and the pressure in chamber 62e begins falling off the pressure in lower portion of second cylinder 47 continues to increase the increasing pressure in cylinder 47 acting in the larger areas of lower portion71 of pilot valve 68 will serve to overcome the force of spring 82. This toggle action will prevent the normal hunting on and off at the pilot valve unseating pressure associated with unloading circuits heretofore used.

When the pressure in the hydraulic system beings decreasing from the pressure prevailing to cause the unloading conditi-on of FIGURE 4, the pilot valve 68 will not shift downwardly at the third pressure which caused it to shift upwardly but will shift downwardly at a lower pressure than the said third pressure. When the pressure i begins decreasing the pressure in the lower portion of second cylinder 47 will likewise decrease. As the pressure is decreased pilot valve 68 will move downwardly closing chamber 62e and thereby cause pressure to begin building up in chamber 62e". The pressure will build up in 62h to a magnitude to urge pilot valve 68 to the position thereof shown in FIGURE 3. Piston 39 will accordingly shift to restore combined downstream fluid iiow from first and second inlet chambers 14 and 24. The differential areas between the intermediate portion 70 and lower portion 71 of pilot valve 68 is selected so that the reseat pressure is lower than the unseating or third pressure referred to earlier herein. It has been found that a ten to twenty percent difference in areas between the larger lower portion 71 and the smaller intermediate portion provides the toggle action referred to with regard to FIGURE 3, and a safe lower reseat pressure for preventing hunting as described in the introductory portion of this description.

While I have shown and described a present preferred embodiment of the invention it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied within the scope of the following claims.

We claim:

1. A pilot operated unloading valve, comprising: a valve body having first inlet means adapted to be connected wtih a first source of pressurized fluid and second inlet means adapted to be connected with a second source of pressurized iiuid; a passageway communicating between said first and second inlet means; pressure responsive closure means in said passageway for blocking communication between said first and second inlet means; outlet means communicating with said first inlet means; a first cylinder intersecting said second inlet means; a second cylinder spaced from said first cylinder; an exhaust passage communicating between said first and second cylinders; a downstream open first branch passage communieating with said first inlet means and having a parallel ow path communicating with portion of said second cylinder; a second branch passage communicating between one end portion of said first cylinder and an intermediate portion of said second cylinder; pressure responsive piston means shiftable in said first cylinder and having a first bore communicating between said second inlet means and the other end portion of said first cylinder and a second bore communicating between said second inlet means and said one end portion of said first cylinder; pilot valve means shiftable in said second cylinder and responsive to first, second and third progressively increasing fluid pressures in said first inlet means to be oriented -when the pressure in said inlet means is below said first fluid pressure in a first position to connect said second branch passage with said exhaust passage through said second cylinder and thereby cause said piston to be positioned for connecting said second inlet means with said exhaust passage while causing said closure means to close to block communication between said first and second inlet means, and further responsive to be oriented when the pressures in said first inlet means reaches said first fluid pressure in a second position to block communication between said second branch passage and said exhaust passage and thereby cause said piston to be positioned to block communication between said second inlet means and said exhaust passage while causing said closure means to open to conneet said second and first inlet means, and yet responsive to be oriented in a third position when said third fiuid pressure is reached to connect said second branch passage with said exhaust passage to thereby cause said piston to be positioned for connecting said second inlet means with said exhaust passage while causing said closure means to close to block communication between said first and second inlet means, and still yet responsive to be oriented in said second position when the pressures in said first inlet means decreases from said third fluid pressure to said second fluid pressure.

2. An unloading valve as set forth in claim 1 wherein said pilot valve means is slidable in said second cylinder; and includes biasing means for urging said pilot valve means toward said one end of said second cylinder.

3. An unloading valve as set forth in claim 1 wherein said pilot valve means includes a spool element having a chamber therein and an intermediate opening communieating between said chamber and said Second cylinder, a pilot valve element shiftable in said chamber; and said spool and said pilot valve element are responsive to said first, second and third Huid pressures in said first and second inlet means, respectively, to be oriented in said first position to connect said second branch passage with said exhaust passage through said second cylinder around a portion of said spool while connecting said second branch passage with said chamber through said opening in said spool and thereby cause said piston to be positioned to connect said second inlet means with said exhaust passage, and further responsive to an increase of said first fluid pressure to be shifted together as a unit to said second position such that said spool will block cornmunicating between said second branch passage and said exhaust passage and thereby cause said piston to be positioned to block communication between said second inlet means and said exhaust passage while causing said closure means to open to connect said second and first inlet means, and yet responsive to an increase of the pressure in said inlet means to said third fluid pressure to shift said pilot valve element to a third position to connect said second branch passage to said exhaust passage through said opening in said spool into said chamber and around a portion of said pilot valve element to thereby cause said piston to be positioned for connecting said second inlet means with said exhaust passage while causing said closure means to close to block communication between said first and second inlet means, and still yet responsive to be oriented in said second position when the pressure in said inlet means decreases from said third fluid pressure to said second fluid pressure.

4. An unloading valve as set forth in claim 3 wherein said pilot valve means includes biasing means for urging said spool and said pilot valve element into said first position.

5. An unloading valve as set forth in claim 4 wherein said pilot valve element is slidable in said chamber and has one end portion extending outwardly of said spool in the direction of the other end of said second cylinder, and wherein said pilot valve element is provided with an intermediate portion having a cross-sectional area less than the cross-sectional area of the other end of said pilot valve element; said areas being of such magnitudes that said pilot Valve element will be balanced when the pressures in said first and second inlet means are at said first and second fluid pressures, respectively, and when said first fiuid pressure increases up to said third fluid pressure.

6. An unloading valve as set forth in claim 5 wherein said first branch passage is provided with throttling means for regulating the pressure of iiuid entering said second cylinder from said first inlet means.

7. An unloading valve as set Iforth in claim S wherein the cross-sectional area of said other end of said pilot valve is between about 5% to 50% greater than the crosssectional area of said intermediate portion of said pilot valve element. v

8. A pilot operated unloading valve, comprising: a housing having a main bore therein; a first inlet passage extending transverse to said main bore and adapted to be connected with a first source of pressurized fluid; a second inlet passage extending transverse to said main bore and adapted to be connected with a second source of pressurized iiuid; an outlet passage transverse to and intersecting said main bore and communicating with said inlet passages; pressure responsive closure means in said bore between said second inlet passage and said outlet passage; a first cylinder intersecting said second inlet passage; a second cylinder spaced from said first cylinder; an exhaust passage communicating with said first cylinder and said second cylinder; a downstream open first branch passage communicating between said first inlet passage and one end portion of said second cylinder; a second branch passage communicating between one end portion of said rst cylinder and an intermediate portion of said second cylinder; a piston slidable in said first cylinder having a first bore communicating between said second inlet passage and the other end of said first cylinder and a second bore communicating between said second inlet passage and said one end of said first cylinder; first biasing means in said first cylinder Ifor urging said piston toward the other end of said first cylinder; a spool element in said second cylinder slidable therein and having a chamber extending therethrough and an intermediate opening communicating between said second cylinder and said chamber; a pilot valve element slidable in said chamber and having one end portion thereof extending outwardly of said spool in the direction of the other end of said second cylinder; second biasing means in said second cylinder for urging said spool and said pilot valve toward said one end of Said second cylinder; said pilot valve element being provided with an intermediate portion having a cross-sectional area less than the cross-sectional area of the other end of said pilot valve, said areas being of such magnitude that when fiuid under a first pressure enters said first inlet passage fluid will flow through said first branch passage to said one end of said second cylinder and fiuid will flow from said second inlet passage through said second bore in said piston through said second branch passage and around said spool to said exhaust and into said chamber in Said spool onto said intermediate portion of said pilot valve element to import a force on said sleeve and said pilot valve which force in concert with the force of said second biasing means will urge said spool and said pilot valve element toward said one end of said second cylinder and fluid will flow from said second inlet through said first bore in said piston to said other side of said first cylinder and the pressure of such fiuid acting on said piston overcome to force the said first biasing means acting on said piston and fiuid will fiow from said second inlet passage around said piston and into said exhaust passage and fluid flow will be blocked by said closure means between said second inlet passage and said outlet passage, and when the pressure of the fluid in said first inlet passage increases above said first pressure fiuid will ow lfrom said first inlet passage through said outlet passage and through said first branch passage to said one end of said second cylinder to urge said spool and said pilot valve element bodily as a unit to a first position toward the other end of said second cylinder to block communication between said second branch passage and said exhaust passage and fluid will flow from said second inlet passage through said first bore in said piston through said second branch passage into said chamber in said spool onto said intermediate portion of said pilot valve element and said piston will be urged by said first biasing means toward said other end of said first cylinder to block communication between said second inlet and said exhaust passage and fluid will flow from said second inlet passage around said closure means through said outlet passage, and when the fiuid in said first inlet passage increases to a third pressure fluid will flow from said first inlet passage through said first branch passage into said one end portion of said second cylinder to move said pilot valve from said first position upwardly of said sleeve to connect said second branch passage with said exhaust passage around said pilot valve and fiuid will flow through said first bore in said piston to said other end of first cylinder to move Said piston toward said one end of said first cylinder to connect said second inlet passage with said exhaust passage and fiuid fiow is blocked between said second inlet passage and said outlet passage, and when the pressure in said first inlet passage decreases to a second pressure said pilot valve will return to said first position to block communication between said second branch passage and said exhaust passage and Huid will thereby flow from said second inlet passage through said first bore in said piston through said second branch passage into said chamber in said spool onto said intermediate portion of said pilot valve element and said piston will be urged by said first biasing means toward said other end of said rst cylinder to block communication between said second inlet and said exhaust passage and fluid will flow from said second inlet passage around said closure means through said outlet passage.

References Cited UNITED STATES PATENTS 2,905,191 9/1959 Kaay 137-108 X 2,971,524 2/1961 Ruhl 137-l08 3,154,921 11/1964 Iunck 137-108 X ALAN COHAN, Primary Examiner U.S. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent ANo. 3,482,590 December 9, 1969 Robert F. Hodgson et al.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column l, line 39, after "providing" insert high fluid flow for fast operation, Column 2, line 3, "hunting" should read "hunting" Column 6, line 7l, "beings" should read begins Column 8, line 75, after "said" insert main Column 9, line 34, after "exhaust" insert passage line 36, "import" should read impart Signed and sealed this 3rd day of November 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr.` WILLIAM E. JR.

Attesting Officer Commissioner of Patents 

